Solidify modifier distorted
The scaling is probably not uniform across the mesh (i.e. X, Y and Z have been scaled to different values in object mode), therefore the "Solidify" thickness varies according to direction.

Do CtrlA > Scale to fix this and this should fix the behaviour of Solidify too.



Example: the mesh (with solidify) is stretched along a single direction. Solidify gets distorted. Then "Scale" is applied and it gets fixed.



at the end it's not a glitch: it's me comparing the effect before and after